The present application relates to resin compositions for protective films, particularly resin compositions for protective films used as protective films for optical discs such as compact discs (CDs), digital versatile discs (DVDs), and the like.
Typically, optical discs of this type are provided with hard coatings on the surfaces of their exterior parts to protect the surfaces of the exterior parts against scratches.
Effective materials for such coatings are inorganic materials having high scratch resistance, but the inorganic materials have the disadvantage that coating solutions thereof are difficult to apply in a small thickness because of high viscosities.
For this reason, studies have been recently conducted to achieve coatings of small thickness by using low-viscosity UV-curable coating materials.
In order to ensure both scratch resistance and good coating geometry in such UV-curable coating materials, it is effective to use coating materials having low shrinkage and low viscosity, but low-shrinkage UV-curable hard coating materials have the disadvantage that solutions thereof has high-viscosity.
A conventional approach to solve this problem is to lower the viscosity of coating solutions by solvent dilution, but this approach increases the number of processes because the step of diffusing diluted solutions is required.
Another possible approach is to prepare a low-viscosity hard coating solution by using a diluent monomer, but this approach may decrease scratch resistance or increase cure shrinkage (warp).
Moreover, it is necessary to select materials allowing light transmission in a necessary wavelength range when hard coating materials of this type are to be used in light-transmitting parts of optical discs.